Alcatraz was a military fort before it became a federal prison. In 1854, the United States government erected a lighthouse on the island. In 1859, the Army established a fort on Alcatraz to defend San Francisco Bay.

During the Civil War [1861-1865], the Army imprisoned deserters, insubordinate soldiers, and Confederate sympathizers on the island. In 1868, the Army established a permanent military prison on Alcatraz.

Soldiers convicted of crimes in court-martials [the military version of civilian criminal trials] could be sentenced to imprisonment at Alcatraz. At first, inmates were housed in various structures that the Army converted for use as prisons. In 1909, the Army demolished much of the original fort, and started building a new prison there.

Because of high operating costs, the Army abandoned Alcatraz in 1934. It turned the facility over to the Federal Bureau of Prisons. The Bureau modernized it into a maximum security prison for high-risk civilian criminals.